Conventional free-space digital optical systems require optical power supplies which generate two dimensional arrays of uniform intensity radiation beams ("beam arrays"). This is more fully described in "Beam Array Generation and Holographic Interconnections in a Free-Space Optical Switching Network," Applied Optics, vol. 32, no. 14, pp. 2512-2518, 1993, by R. L. Morrison, S. L. Walker and T. J. Cloonan, which is incorporated herein by reference. Beam arrays are utilized to illuminate opto-electronic logic devices to perform a host of communication functions, including the transferring of data and the optical encodation of information, for example.
Beam arrays are typically generated by illuminating a processing system designed Fourier-plane phase grating, or hologram, with a laser beam source. A laser beam more particularly is a narrow beam of coherent and nearly monochromatic electromagnetic radiation. Phase gratings are desired in digital optical systems because of their high diffraction efficiency. High diffraction efficiency more particularly is the phase grating's ability to couple a large fraction of impinging light energy into the beams of the beam array. It is desirable to accomplish this with little or no absorption of light intensity by the phase grating. Phase, or surface relief, gratings, also referred to as multiple beam splitters, are generally designed using a programmable processing system that operates to generate a data set representative of the desired phase grating. The generated data set is utilized by a conventional fabrication process to produce the physical phase grating.
One processing system implementation uses an interactive discrete on-axis encoding algorithm, which is more fully described in "Interactive Encoding of High-efficiency Holograms for Generation of Spot Arrays," Optics Letters, vol. 14, no. 10, pp. 479-481, May 1989, by M. R. Feldman and C. C. Guest, and which is incorporated herein by reference. In accordance with this algorithm, one period of the Fourier-plane hologram is divided into an array of rectangular cells wherein each cell imparts one of two fixed phase delays to the incident wave-front. This algorithm, similar to other conventional implementations, is typically inefficient, both in the resources required by, and quality of, the design process. In particular, the required processing resources include large quantities of memory, high input/output throughput and vast amounts of processing time to design satisfactory holograms. Relatively lengthy satisfactory hologram design is particularly commercially unacceptable.